There are two classes of men, namely the devotee and the demon. The Lord selected Arjuna as the recipient of this great science owing to his being a devotee of the Lord, but for the demon it is not possible to understand this great mysterious science. There are a number of editions of this great book of knowledge. Some of them have commentaries by the devotees, and some of them have commentaries by the demons. Commentation by the devotees is real, whereas that of the demons is useless. Arjuna accepts Śrī Kṛṣṇa as the Supreme Personality of Godhead, and any commentary on the Gītā following in the footsteps of Arjuna is real devotional service to the cause of this great science.
(Bhagavad-Gita----4:3----purport).

Arjuna is an accepted devotee of the Lord, so how could he not believe Kṛṣṇa's words? The fact is that Arjuna is not inquiring for himself but for those who do not believe in the Supreme Personality of Godhead or for the demons who do not like the idea that Kṛṣṇa should be accepted as the Supreme Personality of Godhead; for them only Arjuna inquires on this point, as if he were himself not aware of the Personality of Godhead, or Kṛṣṇa.
(Bhagavad-Gita----4:5----purport).

He is like the vaidūrya stone, which changes color yet still remains one. All those multiforms are understood by the pure, unalloyed devotees, but not by a simple study of the Vedas (vedeṣu durlabham adurlabham ātma-bhaktau). Devotees like Arjuna are constant companions of the Lord, and whenever the Lord incarnates, the associate devotees also incarnate in order to serve the Lord in different capacities. Arjuna is one of these devotees, and in this verse it is understood that some millions of years ago when Lord Kṛṣṇa spoke the Bhagavad-gītā to the sun-god Vivasvān, Arjuna, in a different capacity, was also present. But the difference between the Lord and Arjuna is that the Lord remembered the incident whereasArjuna could not remember. That is the difference between the part-and-parcel living entity and the Supreme Lord. Although Arjuna is addressed herein as the mighty hero who could subdue the enemies, he is unable to recall what had happened in his various past births.
(Bhagavad-Gita----4:5----purport).

Therefore, the Lord and the living entity can never be equal in all respects, even if the living entity is as liberated as Arjuna. Although Arjuna is a devotee of the Lord, he sometimes forgets the nature of the Lord, but by the divine grace a devotee can at once understand the infallible condition of the Lord, whereas a nondevotee or a demon cannot understand this transcendental nature. Consequently these descriptions in the Gītā cannot be understood by demonic brains. Kṛṣṇa remembered acts which were performed by Him millions of years before, but Arjuna could not, despite the fact that both Kṛṣṇa and Arjuna are eternal in nature. We may also note herein that a living entity forgets everything due to his change of body, but the Lord remembers because He does not change His sac-cid-ānanda body. He is advaita, which means there is no distinction between His body and Himself. Everything in relation to Him is spirit—whereas the conditioned soul is different from his material body.
(Bhagavad-Gita----4:5----purport).

Arjuna addresses the Lord as Madhusūdana because Kṛṣṇa once killed a demon named Madhu. Actually these questions, which are of the nature of doubts, should not have arisen in the mind of Arjuna, because Arjuna is a Kṛṣṇa conscious devotee. Therefore these doubts are like demons. Since Kṛṣṇa is so expert in killing demons, Arjuna here addresses Him as Madhusūdana so that Kṛṣṇa might kill the demonic doubts that arise in Arjuna's mind.
(Bhagavad-Gita----8:2----purport).

Kṛṣṇa is here advising Arjuna that he should not be disturbed by the different paths the soul can take when leaving the material world. A devotee of the Supreme Lord should not worry whether he will depart by arrangement or by accident. The devotee should be firmly established in Kṛṣṇa consciousness and chant Hare Kṛṣṇa. He should know that concern over either of these two paths is troublesome.
(Bhagavad-Gita----8:27----purport).

Arjuna was born in a saintly royal family. To him also the Lord says, "Take to My devotional service and come quickly back to Godhead, back home." No one should remain in this temporary world, full as it is with miseries. Everyone should attach himself to the bosom of the Supreme Personality of Godhead so that he can be eternally happy. The devotional service of the Supreme Lord is the only process by which all problems of all classes of men can be solved. Everyone should therefore take to Kṛṣṇa consciousness and make his life perfect.
(Bhagavad-Gita----9:33----purport).

The more one hears about the Supreme God, the more one becomes fixed in devotional service. One should always hear about the Lord in the association of devotees; that will enhance one's devotional service. Discourses in the society of devotees can take place only among those who are really anxious to be in Kṛṣṇa consciousness. Others cannot take part in such discourses. The Lord clearly tells Arjuna that because Arjuna is very dear to Him, for his benefit such discourses are taking place.
(Bhagavad-Gita----10:1----purport).

Kṛṣṇa is the Supreme Personality of Godhead, and one should always meditate upon Him and enjoy one's transcendental relationship with Him. He is the supreme existence. He is free from bodily needs, birth and death. Not only does Arjuna confirm this, but all the Vedic literatures, the Purāṇas and histories. In all Vedic literatures Kṛṣṇa is thus described, and the Supreme Lord Himself also says in the Fourth Chapter, "Although I am unborn, I appear on this earth to establish religious principles." He is the supreme origin; He has no cause, for He is the cause of all causes, and everything is emanating from Him. This perfect knowledge can be had by the grace of the Supreme Lord.
(Bhagavad-Gita----10:12-13----purport).

Arjuna herein confirms that persons of faithless and demonic nature cannot understand Kṛṣṇa. He is not known even by the demigods, so what to speak of the so-called scholars of this modern world? By the grace of the Supreme Lord, Arjuna has understood that the Supreme Truth is Kṛṣṇa and that He is the perfect one. One should therefore follow the path of Arjuna. He received the authority of Bhagavad-gītā. As described in the Fourth Chapter, the paramparā system of disciplic succession for the understanding of Bhagavad-gītā was lost, and therefore Kṛṣṇa reestablished that disciplic succession with Arjuna because He considered Arjuna His intimate friend and a great devotee. Therefore, as stated in our Introduction to Gītopaniṣad, Bhagavad-gītā should be understood in the paramparā system. When the paramparā system was lost, Arjuna was selected to rejuvenate it. The acceptance by Arjuna of all that Kṛṣṇa says should be emulated; then we can understand the essence of Bhagavad-gītā, and then only can we understand that Kṛṣṇa is the Supreme Personality of Godhead.
(Bhagavad-Gita----10:14----purport).

The Supreme Lord, Kṛṣṇa, can be known by persons who are in a relationship with Him through the discharge of devotional service, like Arjuna and his followers. Persons of demonic or atheistic mentality cannot know Kṛṣṇa. Mental speculation that leads one away from the Supreme Lord is a serious sin, and one who does not know Kṛṣṇa should not try to comment on Bhagavad-gītā. Bhagavad-gītā is the statement of Kṛṣṇa, and since it is the science of Kṛṣṇa, it should be understood from Kṛṣṇa as Arjuna understood it. It should not be received from atheistic persons.
(Bhagavad-Gita----10:15----purport).

And even if one knows Him as the worshipful God of all demigods, one may not know that He is the supreme proprietor of everything; therefore He is addressed as Jagatpati. Thus the truth about Kṛṣṇa is established in this verse by the realization of Arjuna, and we should follow in the footsteps of Arjuna to understand Kṛṣṇa as He is.
(Bhagavad-Gita----10:15----purport).

The superior devotee is concerned not only for his own understanding but for the understanding of all mankind. So Arjuna, out of his mercy, because he is a Vaiṣṇava, a devotee, is opening for the common man the understanding of the all-pervasiveness of the Supreme Lord. He addresses Kṛṣṇa specifically as yogin because Śrī Kṛṣṇa is the master of the yoga-māyā energy, by which He is covered and uncovered to the common man. The common man who has no love for Kṛṣṇa cannot always think of Kṛṣṇa; therefore he has to think materially. Arjuna is considering the mode of thinking of the materialistic persons of this world.
(Bhagavad-Gita----10:17----purport).

Now, as far as Arjuna is concerned, he says that his illusion is over. This means that Arjuna no longer thinks of Kṛṣṇa as a mere human being, as a friend of his, but as the source of everything. Arjuna is very enlightened and is glad that he has such a great friend as Kṛṣṇa, but now he is thinking that although he may accept Kṛṣṇa as the source of everything, others may not. So in order to establish Kṛṣṇa's divinity for all, he is requesting Kṛṣṇa in this chapter to show His universal form. Actually when one sees the universal form of Kṛṣṇa one becomes frightened, like Arjuna, but Kṛṣṇa is so kind that after showing it He converts Himself again into His original form. Arjuna agrees to what Kṛṣṇa has several times said: Kṛṣṇa is speaking to him just for his benefit. So Arjuna acknowledges that all this is happening to him by Kṛṣṇa's grace. He is now convinced that Kṛṣṇa is the cause of all causes and is present in everyone's heart as the Supersoul.
(Bhagavad-Gita----11:1----purport).